1. Field of the Invention
The present invention relates to methods of extracting hydrocarbon contaminants from underground zones, and more particularly, to such methods for extracting pools of liquid hydrocarbons from subterranean zones including those on and below water tables.
2. Description of the Prior Art
Hydrocarbon contaminants which have leaked into the ground from storage tanks, hydrocarbon processing facilities and the like have heretofore been extracted by a variety of methods such as by vaporizing and removing the hydrocarbons, chemically oxidizing the hydrocarbons, biologically degrading the hydrocarbons and the like. While these and other methods have heretofore been successfully utilized in certain hydrocarbon extraction applications, they are not suitable for use in all of such applications.
When the underground hydrocarbon contaminants are light liquid hydrocarbons such as gasoline which can be evaporated by contact with air, methods which evaporate and extract the evaporated hydrocarbons have been used successfully. Such methods are often referred to as soil vapor extraction methods, and they generally include drilling one or more extraction wells into an underground zone which contains light liquid hydrocarbons evenly dispersed throughout unsaturated ground. A vacuum is pulled in the underground zone containing the hydrocarbons which causes air from the surface and surrounding zones to sweep through the porosity of the ground and through the underground zone containing the liquid hydrocarbons whereby the liquid hydrocarbons are evaporated and extracted by way of the extraction wells.
Soil vapor extraction methods have heretofore also included the injection of steam or combustion gases into a contaminated underground zone by way of an injection well to heat the contaminated ground between the injection well and one or more soil vapor extraction wells. While such methods have been successful in removing evenly dispersed light liquid hydrocarbons, they are not effective in removing hydrocarbons that exist in pools on water tables, below water tables or at the bottom of porous ground formations.
Thus, there are needs for improved methods and processes for extracting liquid hydrocarbon contaminants from underground zones including pools of liquid hydrocarbons.
The present invention provides improved methods of extracting liquid hydrocarbon contaminants from underground zones which meet the above described needs and overcome the deficiencies of the prior art. The methods bring about the removal of evaporatable light liquid hydrocarbons as well as dense liquid hydrocarbons in the form of liquid pools on top of or below water tables or at the bottom of permeable ground formations. The methods of this invention are comprised of the following steps. A hot purge gas is introduced into the underground zone containing liquid hydrocarbon contaminants including a pool of dense liquid hydrocarbons. The hot purge gas heats the underground zone and the liquid hydrocarbon contaminants therein whereby light liquid hydrocarbons in and around the pool are evaporated, and dense liquid hydrocarbons in the pool are evaporated to some extent and the residual is charred, auto-ignited and combusted. The hot purge gas, the evaporated light liquid hydrocarbons and combustion gases from the combustion of the dense liquid hydrocarbons are removed from the underground zone.
The hot purge gas is introduced into the underground zone containing a pool of liquid hydrocarbon contaminants by way of an injection well drilled into the zone. The gases introduced and produced in the zone comprising hot purge gas, the evaporated light liquid hydrocarbons and the combustion gases from the combustion of the dense liquid hydrocarbons are removed from the zone by way of one or more extraction wells drilled into the zone. Vacuums are pulled on the underground zone by way of the extraction wells which bring about the removal of the gases. When the pool of liquid hydrocarbon contaminants is not below ground saturated with water or oil, e.g., the pool of hydrocarbon contaminants is on top of a water table, air is pulled through the porous underground zone containing the pool whereby it vaporizes light liquid hydrocarbons and sweeps the hot purge gas, the vaporized light hydrocarbons and combustion gases out of the underground zone and into the extraction wells. In applications where the pool of liquid hydrocarbon contaminants is below a water table on the bottom of a permeable ground formation, air is included in the hot purge gases for maintaining and controlling the combustion of the dense hydrocarbons.
It is, therefore, a general object of the present invention to provide improved methods of extracting liquid hydrocarbon contaminants from underground zones.
Other and further objects, features and advantages of the invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.